Antibacterial effect of the leaves of Eucalyptus globulus against clinical bacterial isolates

Antibiotic resistance being a major threat to public health, instigated the search for new antimicrobial agents especially in the recognized medicinal plants. In this study the antibacterial effect of the leaves of the plant: Eucalyptus globulus, used in herbal medicine, against clinical Gram positive and Gram negative clinical bacterial isolates was studied. This antibacterial effect was determined using the well agar diffusion and agar dilution methods. Using the well agar diffusion method, the aqueous extract of E. globulus exhibited a weak inhibitory effect evident at a volume of 200 μl against the methicillin resistant and methicillin sensitive Staphylococcus aureus isolates and 2 of the 3 Enterococcus faecalis isolates and at a volume of 300 μl for the Acinetobacter baumannii isolates. On the other hand, the methanolic extract of the plant showed a notable inhibitory activity against methicillin-resistant and methicillin sensitive S. aureus, A. baumannii, Streptococcus pyogenes and 2 of the 3 Enterococcus faecalis isolates. The Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli isolates were resistant to the volumes used of both extracts and were only inhibited at higher concentrations using the agar dilution method. At a ratio of methanolic extract to MHA equal to 0.15, the P. aeruginosa isolates exhibited moderate growth while the K. pneumoniae and E. coli isolates showed weak growth. At a ratio of methanolic extract to MHA of 0.2, the three Gram negative bacteria were completely inhibited. The results of this study highlight the possibility of extracting an efficient broad-spectrum antibacterial agent from the leaves of Eucalyptus globulus.